Can tea bags be home composted?

Back in 2018, Resource explored whether you should put tea bags in your food waste bin.

At that time using non-biodegradable polypropylene (PP) as sealants within tea bags was ‘typical for the market’, with leading tea brand Yorkshire Tea confirming that the company’s tea bag material contained around 25 per cent PP. The article recognised ‘there is understandably some cause for concern about the cumulative effects of microplastic’, which could enter into the waste stream as a result of the application of PP in tea bags.

This risk could be avoided, the article concluded, by either using no tea bag and switching to loose leaf, or swapping to polylactic acid (PLA) tea bags that are ‘100 per cent compostable’.

Now in 2022, the development of biodegradable plant-based PLA has been adopted by national tea brands, including Yorkshire Tea, as a replacement for the non-biodegradable PP alternative. It is advised that these tea bags, once deemed compostable, are placed in food waste caddies for collection – to avoid landfill and to be treated through industrial composting or Anaerobic Digestion (AD).

So what actually is PLA? And why are UK residents specifically instructed to put tea bags into the food waste? What about home compost?

Plant-based plastic

As opposed to many plastics that are made by refining crude oil, PLA is made from plant-derived substances like corn starch and sugarcane. In the past, this material was endorsed by smaller manufacturers and lesser-known brands.

Now, many of the major tea brands have either moved, or are in the process of moving, to PLA – for example, PG Tips states that everything inside its boxes of tea is now plant-based and Twinings confirms that ‘99 per cent’ of its range is now either loose-leaf or made from a plant-derived material.

Yorkshire Tea now uses PLA in most of its tea bags. It is, however, advised to double-check boxes in supermarkets on how to dispose of bags correctly. Although Yorkshire Tea’s tea bags are made from PLA, the company clarifies that ‘plant-based plastics are still plastics’ and whilst a PLA tea bag is ‘biodegradable’ and will completely break down into its natural components, this does not mean they are necessarily ‘compostable’ - a clarification that touches on the complications around terms.

Why can tea bags not go into home compost?

Tea bags vary and can be made of different materials, and although tea can be a helpful addition to compost, there is a risk that placing tea bags in compost will result in adding microplastics to the food chain and harm the growth of composting microbes. As highlighted by Yorkshire Tea, even if the tea bags in question consist of PLA, plant-based plastics are still plastics.

One study assessing the life cycle for PLA (Ghomi et al, 2021) points to the biodegradability of PLA as presenting several end-of-life options for the material, including mechanical recycling, chemical recycling, landfilling, and industrial composting. The study states that ‘it should also be noted that compostability is the same as biodegradability but under aerobic conditions for 6–12 weeks’.

Developing the End of Life (EoL) composting option, the study explains that ‘PLA and its products are biodegradable, but it does not allow for littering them in the environment or self-composting’. This is due to the fact it is difficult for bio-polymers to degrade at natural environment temperature, leading to the conclusion that ‘composting is generally considered one of the worst EoL options due to no energy recovery and low compost quality’.

PLA may break down into carbon dioxide and water within three months in a controlled composting environment, such as an industrial composting facility with heat and decomposing organisms to expedite the process. But, it will take far longer in an at-home compost bin or in a landfill, where it is packed so tightly that no light and little oxygen are available to assist in the process.

Biodegradable plastic residues have also been shown to have potentially stronger negative effects on soil than polyethene (Qi et al, 2018).

As alluded to in Resource’s previous article, the ideal end-of-life for most tea bags – even those consisting of PLA – is to send them, as part of food waste collections, to be treated through the different infrastructure that exists across the UK, and across different local authorities.

However, only one-third of England's district councils and unitary authorities currently offer food waste collections, which won't consistently be introduced across the country until 2025 – a measure proposed in the Environment Bill 2020. Until then, the remainder of the country will need to send their tea bags to landfill, as part of their residual waste stream, regardless of their composition.

Recycling tea bags into renewable energy and biofertiliser

Placing tea bags into the food waste collection means that the energy they contain can be harnessed and repurposed.

In Bristol, where the council first rolled out food waste collections in 2006, food waste is collected by recycling crews and taken to GENeco – an Anaerobic Digestion (AD) plant – in Avonmouth.

Speaking to Resource about the journey that tea bags make to the AD facility, Jenny Harrison, Customer Account Advisor at GENeco, confirmed: “We do accept and recycle tea bags into renewable energy and biofertiliser as part of our anaerobic digestion treatment facility and we recommend you include them in your food waste bin. Anyone who has ever felt revived by a cup of tea knows that they contain energy that can be harnessed.”

In terms of the complications that tea bags pose to recycling – due to the plastic contained within the bag – Jenny says: “We still see lots of contamination come into our hall where individuals and companies have, either deliberately or not, not appropriately sorted their waste. We also do not want to put any packaging barriers on people properly recycling so we put all food waste through a process designed to screen out non-organic materials, which we state must make up no more than 10 per cent of a waste stream. Our biofertiliser output is tested daily to ensure it is meeting quality standards for plastics which it has done so for many years.”

So despite the move by national tea brands to adopt biodegradable PLA, it is still treated as plastic when it reaches the facility.

“It is worth noting here that 'biodegradable' plastic is also removed in our depackaging process which almost certainly includes biodegradable tea bags. The facility struggles to identify the difference between compostable packaging and other kinds of packaging and thus removes everything as contamination. In addition, anaerobic digestion is quite a different process (37-41 degrees C for 18-24 days) to traditional or industrial composting (usually in the presence of oxygen over longer timescales and higher temperatures) which is how most biodegradable packaging is designed to decompose. However, none of the separated plastic goes to landfill, it is then sent to an external energy from waste facility to provide energy for local homes.”

So when tea bags reach GENeco, they will contribute to producing ‘sustainable electricities for homes and communities’.

Although areas outside of Bristol may send food waste to industrial composting facilities, GENeco would “prefer them to undergo anaerobic digestion as we can extract and use the valuable gas given off rather than lose it to the atmosphere. At our specific facility, we also have greater environmental controls and depackaging capabilities at the AD plant.”

To completely avoid the issues regarding plastic contamination from tea bags, whilst still reaping the benefits of placing tea leaves into food waste, Jenny recommends “to those that are able, purchasing a few reusable tea strainers and swapping to loose-leaf tea, popping the used leaf in the food waste and the strainer in the washing up at the end of the day.

“If you are unable to leave bags behind, please continue to put them in your food waste bin rather than your garden compost.”